Interaction between genetic diversity and temperature stress on life-cycle parameters and genetic variability in midge Chironomus riparius populations

Abstract

The genetic diversity of natural populations and the increase in global temperature are becoming important issues in ecotoxicological research. We investigated the combined effects of 3 different temperature levels and 6 different levels of genetic diversity on the life history parameters of Chironomus riparius. Inbreeding and loss of genetic variation are major threats to small and endangered populations. The reduction of fitness due to inbreeding is more severe under stressful environmental conditions. We show that under even a moderate temperature stress, a decrease in genetic variation has important consequences on the fitness of populations. This indicates that the global temperature increase could have serious effects on the distribution and survival of locally distributed or rare species.KEY WORDS: Life-history parameters · Microsatellites · Diptera · Chironomidae · Genetic impoverishment Resale or republication not permitted without written consent of the publisherClim Res 33: [207][208][209][210][211][212][213][214] 2007 The aim of this study was to determine the interaction between temperature stress and inbreeding, using an ectothermic aquatic invertebrate to test if genetically impoverished populations exhibit a higher sensitivity to temperature shifts. We selected a species from the dipterian family of Chironomidae, the non-biting midge Chironomus riparius, representing a model organism with a benthic-associated life cycle. Chironomids are widely distributed in the temperate northern hemisphere and are characterised by a huge ecological tolerance (Armitage et al. 1995). They can be found in hot springs, eutrophic and oligotrophic ponds, lowland rivers, and sub-glacial streams (Pinder 1986). Chironomids have 3 aquatic juvenile (egg, larvae and pupae) and one aerial adult life-stages (Olivier 1971). Previous studies assessing the effect of temperature variation (12-37°C) on chironomid growth patterns concluded that growth was promoted by increasing temperature up to a certain limit (Sankarperumal & Pandian 1991, Stevens 1998, Frouz et al. 2002, Pery & Garric 2006. In contrast, female body size and fecundity decreased with higher temperatures (Frouz et al. 2002, Gong et al. 2002. These studies were all performed with single populations; the additional impact of genetic diversity in connection with the effects of temperature shifts was not investigated. Hence, we tested if the development and reproduction of Chironomus riparius are affected by temperature shifts (± 3°C) and if there is an interaction between these effects and genetic diversity. MATERIALS AND METHODS Test organismsFor the experiments, 6 different Chironomus riparius populations were used (Table 1). One population, with a high inbreeding level (Pop. VI) was obtained from ECT Ecotoxicology, Flörsheim. Five other genetically different populations (Pop. I-V) were derived from different generations of a multi-generation study (under controlled conditions) performed using our inbred inhouse mass culture (GEN-) and a genetically ...

Effects of cadmium on life-cycle parameters in a multi-generation study with Chironomus riparius following a pre-exposure of populations to two different tributyltin concentrations for several generations

“…Nowak et al (2007a) for instance showed that inbreeding and reduced genetic variation lead to increased sensitivity towards Cd-exposure in a laboratory experiment using three midge strains with different levels of genetic variability. This result was confirmed in two similar studies with temperature stress (Vogt et al 2007c;Oetken et al 2009). Furthermore, Nowak et al (2007b) showed that the level of genetic diversity significantly impacts the outcome of chemical exposure studies with different laboratory strains of C. riparius.…”

“…The natural logarithm of time (in days) was taken and the number of emerged midges was cumulated and normalised to percentages for each replicate. Afterwards, a non-linear regression was performed (logistic curve, maximal response 100%) of which the EmT 50 is a parameter (for details see Vogt et al 2007c). This parameter could only be determined for treatments with a mortality below 80%, because in these cases meaningful values were generated.…”

Experimental evidence for niche segregation in a sister species pair of non-biting midges

“…T tests were used in order to reveal significant differences among species within treatments. EmT 50 was calculated according to Vogt et al (2007c).…”

Support for the evolutionary speed hypothesis from intraspecific population genetic data in the non-biting midgeChironomus riparius

“…Additional EmT 50 values at 17, 20, 23, 24 and 288C were taken from the literature [35][36][37]. These data were fitted to an exponential decay function (electronic supplementary material, S1.1).…”